1. Field of the Invention
The present invention relates to an image forming system capable of performing various postprocessing for sheets already recorded in an image forming apparatus body, and more particularly to an image forming system in which one or more types of desired postprocessing units among a plurality of postprocessing units can be selectively attached to the image forming apparatus body and to a single-sheet processing machine arranged in such a way as to be able to be selectively attached to the image forming system.
2. Description of the Prior Arts
Conventionally, there has been disclosed an image forming system in which a postprocessing unit having functions of punching, binding, and folding sheets after image recording can be attached to a copying machine as an image forming apparatus, for example, in Japanese Patent Publication (Kokai) No. 2002-128384. This type of image forming system has a single postprocessing unit capable of handling various postprocessing functions, and therefore it is useful when installed in such an environment that various users make a wide variety of uses of the system such as, for example, in an office. Furthermore, the postprocessing unit is relatively compact in size and thus useful in an office requiring space saving in this regard, too. Since the system enables various postprocessing functions using a single relatively compact postprocessing unit, however, the function levels are not necessarily sufficient when focusing only on individual postprocessing functions. For example, if the image forming system is used as a near-print system, the level need be higher than the level of the postprocessing function required for the image forming system used in an office or the like, but it does not reach the level enough to satisfy the requirement.
Furthermore, for example, if it is used as a print on demand system, the system need not always satisfy all kinds of postprocessing functions, but it is only required to have satisfactory performances of specific postprocessing functions. In other words, if it is used as a print on demand system, specific users use more frequently only specific postprocessing functions more often than various users make various uses.
A consideration is being taken on an image forming system based on an image forming apparatus such as a copying machine or a printer with focusing on a print on demand. Thereby, there has been an attempt of unifying postprocessing units for each postprocessing function and enhancing the performance of the postprocessing function. This type of image forming system, however, is very large in size.